The invention pertains to obscuration-type detectors usable in monitoring a selected region for a predetermined condition such as smoke or intrusion. More particularly, the invention pertains to such detectors which include automatic test or alignment verification circuitry.
Projected beam detectors are known for monitoring a smoke level in a region. Alternately, they can monitor a region for intruders. Such detectors usually include a source of a beam of radiant energy such as a laser or laser diode. The beam is projected across a region to be monitored to a reflector or to a sensor. A reflected beam returns to a sensor.
Outputs from the respective sensor are processed either locally or remotely. Beam strength or intensity incident on the sensor can be compared to projected beam strength or intensity.
Where smoke or an intruder is present in the path of the beam, the beam is obscured and sensor output is indicative of reduced beam strength or intensity incident thereon.
Periodic testing of installed, operational detectors is often required by regulatory agencies. One known form of testing is implemented by having maintenance personal physically at least partly obscure the beam by placing an optical barrier into the beam""s path simulating a desired degree of obscuration. An alarm condition will usually register at the monitoring system""s control unit or panel indicating, depending on the barrier""s level of obscuration, a level of functioning. This process is labor intensive, literally requiring a system walk-through. In addition, it will require a second person at the panel to verify the existence of the expected test condition, and to reset the system or the respective detector.
An alternate known form of testing is electronic. In this process, beam strength or intensity is reduced in clear air simulating an obscuration event. Altered sensor output is detected as a response to the simulated obscuration.
While the above described form of electronic testing is all electronic and does not require a walk-through, it does not test operational functionality of a full strength, partly obscured beam. It may not represent a sufficient and acceptable test in all jurisdictions.
There continues to be a need for test methods and devices for such detectors which overcome the drawbacks and limitations of known approaches. Preferably one or more tests could be automatically carried out using normal projected beam strength. It would also be preferable if such tests could be implemented so as to be both cost effective and to provide operational benefits not available with known approaches.
A projected beam ambient condition detector, usable to monitor smoke, or, the presence of bodies such as human beings, animals or inanimate objects in a region being monitored, includes automatic test equipment. The equipment includes at least one filter interposed, or, interposable in the path of a beam which is being transmitted through a region being monitored.
In the preferred embodiment, the filter is movable by a motor. The motor receives electrical signals to move the filter into the path of the beam for the test condition and out of the path of the beam for normal condition. The filter may have a constant obscuration level or a graduated obscuration. If the filter uses a graduated obscuration, then the test position may be varied to a predetermined obscuration position on the filter. In that way, the test can be adjusted to account for the distances of the projected beam in the detection system.
At a predetermined rate or period, the control circuitry of the projected beam detector can cause a test to be conducted, wherein it will send signals to the motor to move the filter into the beam path to a test position. The control circuitry will measure the signals from the receiver circuitry, and after the test, send signals to the motor to move the filter out of the beam path to a normal position. Based upon the measurement of the signals from the receiver circuitry when the filter is not in the beam path and when the filter is in the beam path, the control circuitry will make a determination if the project beam detector is functioning properly or not. If the measured signals from the receiver circuitry during the test condition are not within predetermined limits, the projected beam detector may not be functioning properly and a trouble condition may be indicated.
The receiver circuitry for the projected beam detection system can be located in a separate housing at the opposite end of the area being monitored. Electrical connections between the two housings would allow the control circuitry to monitor the receiver circuitry. An alternate construction is for the receiver circuitry to be in the same housing as the source of the beam with a retro-reflector used to transmit the light back from the opposite end of the area being monitored.
In another embodiment, the filter is electrically alterable to predetermined obscuration levels. An example would be a filter that is optically transparent with little light loss for normal operation and is altered to obscure on the order of 50% of the light passing through it when in the test condition. In the test condition, the control circuitry sends signals to the electrically alterable filter to change the obscuration to a predetermined value that is only partially transparent or non-transparent. This electrically alterable filter would not need the motor of the preferred embodiment since no moving parts would be required to change obscuration. As in the preferred embodiment, the control circuitry will monitor the receiver circuitry in a similar manner, comparing the receiver circuitry signals between conditions where the alterable filter is transparent and at least partially transparent. Electrically altering the filter accomplishes the same function as the movement of the filter into and out of the beam path in terms of providing different levels of obscuration in the beam path.
It is also possible to test the projected beam detector by having the beam path completely blocked so that no light is transmitted to the receiver circuit. This would represent a xe2x80x9cblockedxe2x80x9d beam condition and where the beam is completely blocked to simulate this condition and to test the ability of the detector to recognize this situation.
Another aspect of this invention is the ability to obscure some transmitted rays of light and not others. A motor, possibly the same one that moves an obscuration filter into the beam path, could move a light blocking assembly into the beam path and restrict the light pattern to a smaller pattern than during normal operation. The restricted light pattern could be one wherein the angle of light being transmitted in the beam""s path is reduced. The benefit of this aspect of the invention is that the alignment of the transmitting beam source and the receiver circuitry can be assessed.
If the transmitter and receiver are perfectly aligned, then the narrowing of the beam width will not cause a change in the signal from the receiver circuit because the same light rays are still traveling between the transmitter and receiver circuitry. However, if they are not aligned then the beam width will result in fewer light rays reaching the receiver circuitry and thus resulting a decrease in the signal from the receiver circuitry. An example of this type of structure to narrow the beam is a member with a beam-limiting hole in it. The hole only allows a predetermined width of light pass through it so it becomes beam width limiting.
This method can also use the electrically alterable approach wherein a light obscuring pattern is electrically produced on a member. In the normal mode, the member does not restrict the width of the beam. In the electrically altered mode, the member becomes opaque except for a hole in the center that allows light to pass through at a narrowed beam width.
In yet another embodiment, a plurality of filters can be carried on a mechanically movable, linear or rotary, support member. Control circuitry can position an appropriately patterned filter in the beam""s path. Sensor output can be compared to one or more expected outputs.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.